POP MUSIC : Going to Extremes : The midyear Top 10 offers more provocative pleasures than major commercial efforts from a wide spectrum of pop visionaries

A veteran British rocker teams up with a string quartet to write some material inspired by Shakespeare . . .

A New York rap trio draws upon the music of jazz heroes Art Blakey, Eddie Harris and Sonny Rollins, instead of James Brown or Sly Stone . . .

An uncompromising cult band from San Francisco turns in song to pop crooner Johnny Mathis for career advice.

Yes, it has been a strange six months in pop, one in which the most inviting works proved to be private pleasures rather than major commercial rallying points. Of the artists on today's list of the 10 best albums so far in 1993, only Janet Jackson is a proven bestseller.

The link between Britain's Elvis Costello, New York's Digable Planets and San Francisco's American Music Club--and such other Top 10 list notables as Polly Jean Harvey, Michael Ivey, J Mascis and Paul Westerberg--is that they are all pop extremists.

Rather than trying to echo the commercial trends of the day, they pursue their own visions, contributing to the creative vitality of pop in ways that may be felt for years to come, whether or not they ever connect with a mass audience. (U2's equally visionary "Zooropa" arrives Tuesday, just past the June 30 eligibility date for today's list. It is reviewed on Page 56.)

1. PJ Harvey, "Rid of Me" (Island). There are echoes of Patti Smith, Sinead O'Connor and almost every other woman who has ever mattered in rock in Polly Jean Harvey's fiercely uncompromising look at sexual desire and control, but that's only part of the story. You also feel the influence and force of such male artists as Bob Dylan (the fearless defiance) and Jimi Hendrix (the blues-based power). A complex, scintillating work. The band headlines the Hollywood Palladium on July 13.

2. Paul Westerberg, "14 Songs" (Reprise). Westerberg is the most gifted American rock songwriter of his generation, and the 32-year-old former Replacements leader delivers a gem in this raw and wonderfully varied solo debut. He can be either passionate and personal--"Things" is about failure to communicate in a relationship--or wickedly funny, as in this slap at the education system: "They teach you to fix what needs to be broke / I say he who laughs first didn't get the joke."

3. Dinosaur Jr., "Where You Been" (Sire). J Mascis is in his late 20s and probably listened to as many Neil Young albums while growing up as Paul Westerberg did, only where Westerberg paid attention mostly to the words, Mascis focused on the guitar workouts with Crazy Horse. And he's as eloquent in his best moments with an electric guitar as Westerberg is with images and wordplay. In his band's most personal and accessible work, Mascis reflects again on relationships and miscommunication.

4. American Music Club, "Mercury" (Reprise). Think of Mark Eitzel, the thirtysomething leader of this San Francisco group, as a punk Leonard Cohen, an uncompromising songwriter inspired by the independence and intensity of punk and the naked confessions of Cohen. The subject matter in the band's major-label debut may be somber, but the music is usually tuneful and there are moments of levity. Don't miss the playful surrealism of "Johnny Mathis' Feet."

5. Elvis Costello and the Brodsky Quartet, "The Juliet Letters" (Warner Bros.). Costello may be an old grouch much of the time, but you've got to love his disdain for pop convention and career consequence by letting some letters addressed to Shakespeare's Juliet inspire him to do something as stubbornly offbeat as joining with the British string quartet to write and perform an entire album of their own imaginary letters. The surprise is that this is Costello's freshest work in nearly a decade.

6. Digable Planets, "Reachin' (A New Refutation of Time and Space)" (Elektra). This New York trio, best known for the hit single "Rebirth of Slick (Cool Like Dat)," is part of a new wave of alternative rappers who are broadening the music's base--in the Digable's case, with a jazz-accented approach that is both urban and urbane. On record and onstage, the group exhibits the kind of strong appeal to intellect and winning flair for experimentation that could make it the Talking Heads of rap.

7. Basehead, "Not in Kansas Anymore" (Imago). Just what is Basehead's true style? Is it rap, R&B, funk, satiric pop? And why hasn't Basehead (the moniker adopted by Michael Ivey) made it into the national Top 100 with either of his wonderfully provocative and appealing albums? Why doesn't the crowd that has grown weary of what's-his-name--the guy from Minneapolis--check out Basehead's alternately goofy and biting social observation?